The present invention relates to paper feeding devices that can be applied in apparatuses such as image forming apparatuses that carry out predetermined processing on sheets such as papers, and particularly relates to paper feeding devices in which a pickup roller pulls out an uppermost positioned sheet of loaded sheets and a paper feeding roller transports the sheet pulled out by the pickup roller, and image forming apparatuses provided with these paper feeding devices.
Generally, a paper feeding device is provided in an apparatus such as an image forming apparatus that carries out predetermined processing on sheets, and this paper feeding device is provided with a paper feeding mechanism that feeds the sheet positioned at an uppermost portion of the loaded sheets in order sheet by sheet toward a transport path.
The paper feeding mechanism may be provided with a pickup roller for pulling out an uppermost positioned sheet of the loaded sheets, and a paper feeding roller for transporting the sheet pulled out by the pickup roller.
In this regard, when sheets such as papers are left exposed to open air or for example, when sheets are left loaded in a sheet housing portion, the sheets sometimes curl due to the effects of humidity or temperature or the like. Furthermore, for example, curling may occur in which edge portions become gradually higher than a central area in a sheet transport direction. When this happens, the following problems may occur.
Generally, curling occurs easily in sheets depending on ordinary ambient environment conditions. For example, there are cases of environment conditions of a low temperature and low humidity or a high temperature and high humidity, more specifically, there are cases of a low temperature and low humidity of 10° C., 20% RH, or a high temperature and high humidity of 30° C., 85% RH. In particular, in cases where curling has occurred in sheets of a certain thickness having a basis weight (grammage) of 100 g/m2 or greater such as firm cardboards and glossy papers or the like, problems occur of sheet blockages (hereinafter referred to as jamming).
Hereinafter, description is given regarding problems in feeding caused by sheet curling according to a paper feeding device provided with a pickup roller and a paper feeding roller. It should be noted that the following description sets forth an example of a case using a rotating board as a loading member capable of being loaded with sheets that is rotatable on an axis along a horizontal direction orthogonal to a sheet transport direction.
FIG. 7A and FIG. 7B and FIG. 8A and FIG. 8B are schematic views for describing a conventional paper feeding device 120 provided with a pickup roller 202 and a paper feeding roller 203. FIG. 7A shows a state in which sheets P, which are not curled, have been lowered within a sheet housing unit 80 and FIG. 7B shows a state in which the uncurled sheets P are being transported after being raised in the sheet housing unit 80. Furthermore, FIG. 8A shows a state in which sheets P, which have curled, have been lowered within the sheet housing unit 80 and FIG. 8B shows a state in which the curled sheets P are being transported after being raised in the sheet housing unit 80. It should be noted that the dashed line in FIG. 8B shows a transport trajectory of the sheet P leading edge.
In the paper feeding device 120, when the rotating board 121 is caused to rotate from a state shown in FIG. 7A so as to approach the pickup roller 202 and a bundle of regular, uncurled sheets P is raised by the rotating board 121, an uppermost positioned sheet P contacts the pickup roller 202, and when the sheets P are further raised, a detector piece 207, which is a second detection member that moves integrally with the pickup roller 202 is detected as shown in FIG. 7B by a photosensor 208, which is a first detection member, and the raising of the sheets P stops. Then, the pickup roller 202 feeds out the sheet P from the sheet housing unit 80 to a nip portion γ between the paper feeding roller 203 and a separator roller 204, and the sheets P are transported sheet by sheet.
In this regard, a transport guide member 206 for example is sometimes provided between the pickup roller 202 and the paper feeding roller 203 to smoothly guide the paper P from the pickup roller 202 to the paper feeding roller 203.
Accordingly, when the sheet P has curled due to the effects of humidity or temperature or the like, the sheet P may contact a portion of the transport guide member 206 during transport of the sheet P as shown in FIG. 8A and FIG. 8B (see a portion in FIG. 8B). With a downstream side edge portion in the transport direction of the sheet P given as leading edge portion P1, when the leading edge portion P1 of the curled sheet P is transported while in contact with the transport guide member 206, there is a risk that the transport force will be reduced due to the frictional load at the contact portion α between the sheet P and the transport guide member 206. Due to this, paper feeding problems may occur such as paper feeding delays or jamming due the leading edge portion P1 of the sheet P being obstructed.
In order to improve the transport force of the sheets, JP 2003-171026A (patent document 1) proposes a paper feeding device that is provided with various paper feeding rollers for separation and for drawing in sheets, which are rotationally driven while pressing against an upper surface of the sheets loaded on the paper feeding platform and arranged with intervals in the paper feeding direction, and these paper feeding rollers are arranged in a width direction central area of the paper, and assistive paper feeding rollers of a lower rigidity than the paper feeding rollers for drawing in are arranged on a same axis with intervals in the paper width direction at the end sides of the paper feeding rollers for drawing in.
However, in the paper feeding device described in patent document 1, in the case where the transport guide member is provided between the paper feeding roller for drawing in and the paper feeding roller for separation as in the configuration shown in FIG. 7A, even if the assistive paper feeding rollers are provided on a same axis as the pickup roller, contact of the curled papers to the transport guide member is not avoided, and it is difficult to prevent occurrences of paper feeding problems such as paper feeding delays or jamming or the like caused by curling.
Furthermore, configurations have been proposed in which a roller belt is attached at an outer circumferential region between the paper feeding roller and the pickup roller, thereby applying a transport force to the curled sheets by the belt transport. In paper feeding devices having this configuration, by attaching the roller belt at an outer circumferential region between the paper feeding roller and the pickup roller, curled sheets move with the roller belt when contact is made with the roller belt, and in this way a transport force can be applied to the sheet.
Further still, JP 2002-37465A (patent document 2) proposes a paper feeding device in which a transport belt is wound around a transport direction downstream side pulley and an upstream side pulley so as to surround a negative pressure generating device that generates a negative pressure at a bottom surface, and the recording papers are drawn in and transported due to the negative pressure.
However, in conventional paper feeding devices in which a roller belt is attached between the paper feeding roller and the pickup roller, although a transport force can be applied to curled sheets, there is also a problem such as the following.
Namely, the paper feeding roller and the pickup roller are rotated in synchronization due to the roller belt attached therebetween. For this reason, even after the sheet has passed it, the pickup roller continues to rotate in cooperation with the rotation of the paper feeding roller. Consequently, since it unfortunately rotates in cooperation with the paper feeding roller even after the uppermost positioned sheet has been fed by the pickup roller, a new problem occurs in that a next sheet loaded on the loading member is picked up by the rotation of the pickup roller working in cooperation with the paper feeding roller.